My U.S. Pat. No. 4,917,708, issued Apr. 17, 1990, discloses an indirect calorimeter, or oxygen consumption meter, which may be used to measure the resting energy expenditure of a subject. This measurement is important for determination of the proper caloric content for feedings of hospitalized patients and also is useful in connection with weight loss diets since the basal energy requirement may vary during the period of the diet. Similarly, knowledge of caloric expenditure and oxygen consumption during exercise are useful for cardiac rehabilitation and athletic training.
My previous patent discloses a calorimeter which utilizes a unidirectional flow meter operative to generate electrical signals proportional to the respiratory gases passing through it, a carbon dioxide scrubber operative to remove CO.sub.2 from the exhaled gas and valving and conduits connecting the flow meter and the scrubber between a source of respiratory gases, which may be either the ambient air or some form of positive pressure ventilator, and a patient mouthpiece. The inhaled air has a negligible content of carbon dioxide and the exhaled gas contains lung-contributed carbon dioxide of essentially the same volume as the oxygen consumed by the subject. Accordingly, the difference in volumes between the inhaled and scrubbed exhaled gases passed through the flow meter provides an indication of patient's oxygen consumption. By integrating these differences over a test period, which may last for several minutes, an accurate measurement of the subject's oxygen consumption during the trial may be obtained.